The present invention relates generally to water filters and more particularly to a cyst-reduction water filter delivering a substantial water flow rate at low (gravity-assisted) water pressures. Such filters are of particular interest for applications such as gravity flow filter cartridges in water carafes.
Gravity flow filtration units continue to gain in popularity as consumers become concerned about the quality of available drinking water supplies. Carafe gravity flow units effectively address this concern because of their relatively low cost and perceived efficiency in removing unwanted tastes, odors, and harmful pollutants.
Operation of these units is simple and convenient. Water is simply poured into the top of the unit and is allowed to trickle through a replaceable filter cartridge to a treated water reservoir for later use. The filter cartridges are typically packed-bed units containing carbon pellets for the removal of adsorbable/catalyzable constituents such as chlorine and organics, and ion exchange resins for the removal of metal ions such as lead. Bacteriostatic agents such as silver may also be present. Although gaining in acceptance, filter units presently available for use in gravity flow filtration systems suffer from a number of disadvantages. Packed bed systems typically develop preferential flowpaths within the bed, resulting in less than optimal use of the available adsorbents and exchange media and correspondingly decreased purifying effectiveness and service life. They also tend to release fine adsorbent particles into the treated water during initial use.
Even more important to the consumer is the need to maintain adequate water flow rates even as designs for more efficient particle removal are developed. Gravity-assisted water flow rates through the filters are quite limited even at maximum acceptable filter cartridge sizes. Increasing the particle removal efficiency of the cartridges would likely involve more tightly packed filtration media or special membranes, both of which would be expected to further reduce gravity flow rates. Similarly, commercially available membrane filters capable of effective cyst removal do not generally provide rapid filtration. Thus, given present commercial flow rate requirements, no practical way to achieve the removal or reduction in concentration of such fine biological impurities as cyst particles (&lt;4 micrometers in diameter) in a gravity flow filtration environment has yet been identified.
Fluid filtration elements comprising plugged honeycomb filters are well known in the art. U.S. Pat. No. 4,329,162 and published European patent application EP 0745416, for example, describe the use of such filter elements for the removal of particulates from vapor, water and other fluid streams. However, up to the present, no adaptation of such filters has been identified or considered which would offer the capability of removing very fine particulate biological contaminants such as cysts from a water stream while still offering acceptable water filtration rates under the low pressure (gravity feed) conditions found in water carafes.